Storable isocyanate-modified polyesters



STORABLE lsfiilYANATE-MfiDlFlED POLYESTERS Nelson V. Seeger, CuyahogaFalls, and Thomas G. Mastin, Akron, Ohio, assignors, by mesneassignments, to The Goodyear Tire & Rubber (Iompany, a corporation ofOhio No Drawing. Application September 29, 1952, Serial No. 312,162

Claims. (Cl. 260-75) This invention relates to synthetic polymericmaterials and to methods for preparing the same. More particularly, itrelates to organic diisocyanate-modified polyesters and polyesteramideswhich possess elastomeric, rubber like qualities and to improved-methodsfor their preparation.

The modifying of linear polyesters and polyesteramides with organicdiisocyanates is known in the art. The polyesters are formed by thecondensation of a dibasic carboxylic acid with a glycol. Thepolyesteramides are formed by the condensation of a dibasic carboxylicacid with a mixture of a glycol and an amino alcohol and/ or a diamine.The condensation reaction proceeds with the elimination of water toyield a linear polyester or polyesteramide which is usually viscous,syrupy, or wax-like at room temperature.

As is determined by the materials and amounts thereof used in itsformation, the polyester or polyesteramide may contain terminalcarboxyl, hydroxyl, or amino groups depending upon Whether an acid, aglycol, an amino alcohol, or a diamine was the last compound to react inthe formation of the linear molecule. The polyester or polyesteramide isthen lengthened further by the reaction between these terminal groupsand an organic diisocyanate with the formation of what may be referredto as a chainextended polymer. The linkages formed by the reaction ofthe terminal groups of the polyester with the diisocyanate are aurethane linkage (OL ll I) in the case of a terminal -OH group,principally an amide linkage 0 ll N- in the case of a terminal --COOHgroup, and a substituted urea linkage i l l (-NON-) in the case of aterminal -NH2 group. Since each of these linkages and, in the case ofpolyesteramides, the

amide groups, contain hydrogen available for reaction with additionaldiisocyanate, it is possible to cross-link States Patent ice which maketheir use as synthetic rubbers impractical and undesirable. Inparticular, the known rubber-like" compositions have not possessed thatdegree of processibility required in the fabrication of rubber orrubber-like products. In addition, the known compositions have cured orset up in a relatively short time after their preparation, with theresult that the uncured material cannot be stored for indefinite periodsbetween the time it is prepared and the time it is used. It is thereforean object of this invention to provide a method for. the preparation ofhighly elastic organic diisocyanate-modified polyesters andpolyesteramides which possess processing qualities similar to those ofuncured natural rubber and which may be stored in the uncured state overlong periods of time without hardening or curing. It is a particularobject of this invention to provide organic diisocyanatethechain-extended polymer at various points along its modified polyestersand polyesteramides which possess not only processing and agingcharacteristics similar to those of uncured natural rubber but alsooutstanding physical properties in the final vulcanized state. Stillanother object of this invention is to provide a method for the curingof these processible, storable, modified polyesters and polyesteramides.Other objects will appear as the description proceeds.

According to the invention it has been found that there are severalcritical limitations and requirements in the preparation of thepolyester or polyesteramide itself, the chemical nature of the linkagesformed between the diisocyanate and the terminal groups of the polyesteror polyesteramide, and the type and amount of diisocyanate used tochain-extend and possibly cross-link the polyester or polyesteramide,all of which limitations and requirements must be met in order toproduce a rubber-like material which has the desired processing andaging properties in the uncured state and valuable physical propertiesin the final cured state.

The unmodified polyester is prepared in its simplest form from twobifunctional ingredients, one being a dibasic carboxylic acid and theother being a glycol. The particular polyesteramides, with which thisinvention is concerned, are those formed from the reaction of a dibasiccarboxylic acid with a mixture comprising a glycol and an amino alcoholor a diamine. In addition, a Wide variety of complex polyesters andpolyesteramides may be formed by the reaction of a plurality of acids,glycols, amino alcohols, or diamines. In the preparation of polyesters,it is possible to use ester mixtures such as a physical mixture ofvethylene adipate and 1,2-propylene adipate as well as mixed esters suchas that resulting from the reaction of a mixture of ethylene glycol and1,2-prr. pylene glycol with adipic acid. The reaction proceeds with theelimination of water to yield a long chain molecule containing asuccession ofester or esteramide groups in the chain. The ester andesteramide groups may be illustrated by the following radicals:

from a glycol and a diamine R in all instances denotes a divalentorganic radical such as a hydrocarbon radical. In the preparation of thepolyester or polyesteramide it is possible to obtain products of varyingmolecular weight, depending in part upon the=moleeular weight. of thereactants and in part upon the degree, of, polymerization. of the.reactantsv or. the number of ester or esteramide units in the polyesterof polyesteramide chain. While the average molecular weight of the:polyester. or. polyesteram'ide Willi of course vary depending=upon:theparticular acids, glycols, aminoalcohols and diamines. used; it has nowbeen found that the average number-of these ester. and esteramidegroupspresent in the:polyesten orpolyesteramide' chainmust-be heldwithin certain limits in order to: permit the subse-* quent modificationwith diisocyanate toyield a proces sible, storable polymer. Aconvenient' metho'd of measuring the degree: of polymerizationof thepolyesteror polyesteramide is to determine the" average number ofcarboxyl, hydroxyl, and amino groups in a given amount of thelinear-extended polyester'or po'lyesteramide: The' acid number(milligramsof: KGH per gram-of polyester or polyesteramideusing'phenolphthalein as an indicator) is a measure of the number ofterminal carboxyl' groupsin-the polyester or polyesterarnide. Thehydroxyl num ber, which isa measureofthe: number oftermin'al hy droxyland aminogroupstaken: together; is determined by adding pyridine andacetic anhydride to the polyester or polyesteramide and titrating theacetic acid formed with KOI-Las described in- Ind. Eng. Chem. Anal; Ed";16; 54l'-49-and in lndi Eng;-Chem. Anal. Ed l 7',-394 (1945).The-hydroxyl number is defined as-milligramsof KOH per gram of polyesteror polyesteramidei The sum of the acid number and hydroxyl-numbe'r,which-will be referred:to-as -the reactive numbenis an'indication of theaverage'number ofterminal groups present in the-polyester orpolyesterami-de whichin turnis an indication of the'numb'er of moleculesin the mass and thedegree'of polymerization.- A polyester orpolyest'eramide containing long chain molecules will have arelativelylow reactive number, while a polyester or polyesteramide. containing'short-chain molecules will possess a higher reactive number.

According to, the-practice of the present invention, a rubber-likepolymer is produced from a polyesteror polyesteramidehaving a reactivenumberfrom 30 to 152. lnpreferred practice a polyester or polyesteramidehaving a reactive number from 50 to 65 -is used. tion, for thepurposes-of this invention, the acid number, going to makeupthe'reactive number-,isheld to a maximum of. 12 sincepolyesters orpolyesteramides having an acid number in excess of 12 will'pro'ducediisocyanate modified polymers which are too tough to process satis--factorily. 'I he acid'number is conveniently controlled by providing anapproximate 20 mol percent excess of glycolraminoalcohol, or diamineinthe preparation of the polyester or polyesteramide.

The number ot hydrogen-b'earing amino-groups inthe polyesteram'idestisan additional critical feature applying to. theaprepa'rationofrubber-like diisocyanate-modifiedpolyestera'midesl It has been foundthat polyesteramides produced from amino alcohols ordiamines donot yieldprocessible polymers When-modified with certain diiso-- cyanates if thenumber of NH2 groups present in the reacting mixture exceeds 30% of thetotal number of hydrogen-liberating groups present in. the reactingmixture. This, in efiect, means that where amino alcohols are used, themaximum amount permissible;;is, 60-rmol' percent, the other 40 molpercent being a glycol. In the case of diamines, a maximum of 30 molpercent is permissible. In the case of mixtures of" glycols, anddiamines, the number of -NH2 groupspresentmust be thereof which may'beused. It has'been set, forth. above.

that the natl fr of the; modified polymer, ,Will dependtupon.

In addi 4. the amount of diisocyanate used to chain-extend andcross-linkthe polyesten It-hasnowbeen discovered-that the production ofa processible, storable rubber-like polymer involves not only thedetermination of the critical amounts of diisocyanate to be used butalso the fact that a particular critical range of the amount ofdiisocyanate may beused when modifying polyesters and polyesteramideswith some, but not all,v diisocyanates. The particular diisocyanateswith which this invention is concerned are 2,4 tolylene diisocyanate,hexamethylene diisocyanate, and tetramethylene diisocyanate. For thepurpose of this invention these diisocyanates must be used in an amountranging from 1.00 to 1.20 mols per mol of polyester or polyesteramide. Apreferred range is from 1.00 to 1.10 molsofdiisocyanate per mol ofpolyester or polyesteramide. Smaller amounts will produce soft, stickypolymers which will not process satisfactorily in the usual rubberfabricating operations. Greater amountsproduce' tough polymers whichwill notprocess satisfactorily and which WlllhaldBfl or cure upon aging.It is possible to use a mixture'of the diisocyanates-indicated in thepreparation of the r ubberlike polyesters and polyesteramides so long asthe-total amount of diisocyanate used falls within the range indicated.While certaindiisocyanates will not produce the desired-results if usedin an amount covered by the'critical range specified, it is-to' beunderstood that those listed are not necessarily the only diisocyanates.which are operative for the purposes of this invention but ratherrepresent those which-have actually been tested and-found to produeethedesiredre'sults when employed in an amount covered by thecriticalrange indicated.

After the processible storablepolymer has been formed, it is preparedfor curing by adding more diisocyanate or other conventional curingmaterials such as alkyl ethers of hexamethylol melamine with a2,4-dihalo naphthol as" accelerator. Polyisocyanates, such as4,4,4-triisocyanto triphenyl methane, 1,3,5-triisocyanto benzene, and2,4,6-triisocyanto toluene, may also be used to effect a cure. Anyorganic diisocyanate, polyisocyanate or mixtures of diisocyanates,polyisocyanates, or both may be added in this step. It may be'the sameoradififerent diisocyanatethanthatusedin the formation of theprocessiblepolymer, or it-maybe a diisocyanate other than those listed.If" 2,4'-tolylene diisocyanate isto be used as a curing agent, aconvenient method ofadding it is in the form of its dimer of thefollowing formula The dimer is less toxic than the monomeric material,permitting the use of the dimer in open-mill mixing. The amount ofpolyisocyanate added'to etfect a cure must be controlled so as toprovide a. total number of NCO equivalents, including that added in theformation of the processible polymer,- ranging from 2.80 to 3.20equivalents: of- -NCO per. mol of polyester or. polyesteramide. Smalleramounts ofpolyisocyanate.added to cure the. polymer will result in anuncured product. The use of greater amounts. is, a waste of material.with no improved properties inthe cured product, andinsome cases pro--duces a cured polymer having properties more resinous than rubber-like.

If a triisoeyanate or tetraisocyanate is used to effect a cure,. not asmuch material, on a molbasis, need be usedsince thecuring orcross-linkingof the linear molecules. dependsupon the ;N CO groupspresent in the curing agent. For example, if 0.40 mols of adiisocyanate; gives ,a sat-isfactory cure oi at diisocyanateanodifiedpolyester. or polyesteramide, the;- use--ofapproximately 0.20 mols of atetraisocyanate will result in a similar state of cure.

The actual curing of the polymer is accomplished by methods familiar tothose skilled in the art. The time and temperature required to effectthe best cure for any particular polymer will, of course, vary as is thecase with conventional natural rubber compounds. The cure, for bestresults, should be accomplished by the use of dry heat since exposure ofthe polymer to hot water or steam results in a partial degeneration ofthe cured material.

The following examples, in which parts are by weight, are illustrativeof the preparation of the polyester and polyesteramides and of thediisocyanate-modified polyester and polyesteramides according to theteachings of this invention.

EXAMPLE 1 Preparation of a typical polyester Adipic acid (3515 parts)was placed in a 5-liter, 3- necked flask fitted with a stirrer,thermo-co-uple well, gas inlet tube, distilling head, and condenser. Tothe acid were added 1064parts of ethylene glycol and 869 parts ofpropylene 1,2 glycol. The molar ratio of dibasic acid to glycol is1:1.19. The mixture was heated to 130-160 C. until most of the water haddistilled off. The temperature was then gradually raised to 200 C., thepressure being gradually reduced to 20 mm. and nitrogen being bubbledthrough the melt. After 23 /2 hours a soft white waxy solid wasobtained. Determinations showed the acid number to be 3.5 and thehydroxyl number to be 58.6.

EXAMPLE 2 Preparation of the diisocyanate-modified polymer A quantity ofpolyester was prepared from adipic acid, ethylene glycol, and propylene,1,2 glycol according to the general method and in substantially the sameratios as shown in Example 1. This polyester had an acid number of 3.1and a hydroxyl number of 55.6. After heating 200 parts of this polyesterto 120 C. in an iron kettle, 2,4-tolylene diisocyanate (20.11 parts of99.7% purity or 1.10 mols of diisocyanate per mol of polyester) wasadded. After minutes of mixing, the material was poured into a waxedaluminum tray and baked for 8 hours at 120 C. The resulting polymer hadexcellent processing characteristics on a rubber mill.

EXAMPLE 3 Preparation of cured polymer The diisocyanate-modified polymer100 parts) prepared according to Example 2 was mixed with 5.52 parts of4,4 diphenyl diisocyanate on a rubber mill, bringing the total amount ofdiisocyanate present in the cured compound to 1.59 mols per mol ofpolyester. Test sheets cured for 60 minutes at 300 F. showed thefollowing physical properties:

Tensile 2600 lbs./sq.in. Elongation 710%. 300% Modulus 300 p. s. i.

The table shown below tabulates selected examples of polyesters anddiisocyanate-modified polyesters which were prepared according to thepractices of this invention and according to the general procedureoutlined in Examples l and 2.

Poly- Hydroxyl Acid Diiso- R Example ester No. No. cyanate Value Ratmg A55. 6 3. 1 A 1.0 Excellent. A 55. 6 3. 1 A 1. 1 Very good. A 55. 6 3.1A 1. 2 Good. A 55. 6 3.1 B 1. 1 Very good.

Polyester A80 mol percent ethylene glycol20 mol percent propylene1,2glycol100% adipic acid.

Diisocyanate A2,4-tolylene diisocyanate; B-hexamothylene d1- lsocyanate.

* Mols of diisocyanate per mol of polyester.

The rating indicated for each polymer is based upon its behavior on arubber mill in relation to its processibility on the mill and on otherrubber fabricating equipment. The polymers described in the table havebeen found to age at room temperature for periods in excess of one yearwith little or no apparent change in their processing characteristics.

In addition to the specific materials shown in the experimentalexamples, a variety of other acids, glycols, amino alcohols and diaminesmay be used. Any dibasic carboxylic acid, preferably those whosecarboxyl groups are attached to terminal carbons, may be used to formthe polyester or polyesteramide, including succinic, glutaric, adipic,pimelic, suberic, azelaic, sebacic, malonic, brassylic, tartaric,maleic, malic, fumaric, dilinoleic, thiodibutyric, diphenic,isophthalic, terephthalic, hexahydroterephthalic, p-phenylene diacetic,dihydromuconic, and B-methyladipic acids. For best results theunsaturated acids should be used in mixture with a saturated acid in anamount not to exceed 5 mol The presence of a small amount ofunsaturation in the polyester or polyesteramide is often desirable ifcheaper curing or cross-linking agents such as for example, sulfur,benzoyl peroxide, or tertiary butyl hydroperoxide are to be used. Higherdegrees of unsaturation in the polyester or polyesteramide result incured polymers which do not have the outstanding physical propertiespossessed by the polymers produced from polyesters or polyesteramidescontaining no unsaturation or a relatively'small amount of unsaturation.

Any glycol may be used in the formation of the polyesters orpolyesteramides including ethylene, propylene 1,2, propylene 1,3,diethylene, triethylene, tetramethylene, pentamethylene, hexamethylene,decamethylene, dodecamethylene, and N,N-diethanolaniline.

Any amino alcohol having at least one hydrogen atom attached to theamino nitrogen atom may be employed including ethanolamine,3-amino-propanol, 4-aminobutanol, 6-amino-hexanol, 10-amino-decanol.

Examples of the diamines which may be used are ethylene, propylene 1,3,propylene 1,3, tetramethylene 1,4, hexamethylene 1,6, decamethylene1,10, piperazine, isopropyl aminopropyl amine, and 3,3 diamino dipropylether. I

in addition to the examples already shown, listed below are thereactants which are used to form particular polyesters andpolyesteramides which when modifiedwith diisocyanate according to thepractice of this invention will produce processible, storable polymers.

1. Ethylene glycol plus adipicv acid. 2. Propylene. glycol 1,2 plusadipic acid. 3. Ethylene glycol mol per cent), propylene glycol 1,2 (20mol per cent) plus adipic acid. 4. Ethylene glycol (80 mol per cent),propylene glycol 1,2 (20 mol per cent) plus azelaic acid. 5. Ethyleneglycol (80 mol per cent), propylene glycol 1,2 (20 mol per cent) plussebacic acid. 6. Ethylene glycol (80 mol per cent), propylyene glycol1,2 (20 mol per cent) plus dilinoleic acid (20 mol per cent), adipicacid (80 mol per cent). 7. Ethylene glycol (80 mol per cent), glycerinemonoethyl ether (20 mol per cent) plus adipic acid. 8. Ethylene glycol(80 mol per cent), butylene glycol 1,4 (20 mol per cent) plus adipicacid. 9. Ethylene glycol (80 mol per cent), propylene glycol 1,3 (20 molper cent) plus adipic acid.

Ethylene glycol (80 mol per cent), pentane diol 1,5

(20 mol per cent) plus adipic acid.

Ethylene glycol (80 mol per cent), glycerine monoisopropyl ether (20 molper cent) plus adipic acid.

l2. Ethylene glycol (80 mol per cent), propylene glycol 1,2 (from 18 to5 mol per cent), ethanol amine (from 2 to 15 mol per cent) plus adipicacid.

13. Ethylene glycol (80 mol per cent), propylene glycol 1,2 (20 mol percent) plus maleic acid (from 3 to dmol-per. cent) ,.adipic acid (from9-7 to 94 mol per cent) Ethylene glycol. (80 mol per cent), propyleneglycol 1,2 (from- 19 to 17 mol per cent), piperazine (from 1 m3 mol percent) plus adipic acid.

Anyof theabove materials will produce polyesters orpolyesteram'ide'which' when-prepared and treatedaccordingtoithepractice'of this invention will yield-processible,storable'polyrners'after reaction with any of thefollowing'diisocyanates: 2,4-tolylene diisocyanate, hexamethyl enediisocyanate ,and tetramethylene diisocyanate.

Of particular interest are the rubber-like polymers resulting frompolyethylene adipate modified by 2,4- toly-lenediisocya'nate,hexamethylene' diisocyanate, tetramethylene diisocyanate, or mixturesthereof, polypropylene 1",2' adipate modified by 2,4-tolylenediisocyanate, hexam'ethylene diisocyanate, tetramethylene diisocyanate,or mixtures thereof, polyethylene (80 mol per cent) propylene 1 ,2 20mol per cent) adipate modified by 2,4-tolylene diisocyanate,hexamethylene diisocyanate, tetramethylene' diisocyanate, or mixturesthereof, polyethylene (80- mol per cent) propylene 1,2 (20 mol per cent)azelate'modified by 2,4-tolylene diisocyanate, hexamethylenediisocyanate, tetramethylene diisocyanate, or mixtures thereof, andpolyethylene (80 mol per cent) propylene 1 ,'-2"(fro'm 19'to 17"mol percent) piperazine (from--1'to'-3 mol percent) adipate modified-by2,4-tolyl'-- ene diisocyanate, hexamethylene diisocyanate,tetramethylene diisocyanate, or mixtures thereof.

The' elastomeric' polymers prepared according to the practices-ofthis-invention are, ingeneral, useful in those application's wherenatural rubber orrubber-like materials areuse'dt- Iii-particular theymay be'used in tires, belts, hose, sheet packing, gaskets, moldedgoods-floor mats, dipped goods, sheeting, tank lining, soles, heels,covered rolls, and other mechanicala'nd industrial goods;

Ethylenevglycol (80.mol percent), propylene glycol Thisapplication is acontinuation-in-part of our copending application, Serial No. 170,056,filed June 23-, 1950,- now abandoned- While certain representativeembodiments and details have been shown. for the-purposeof illustratingthe invention, it will be apparent to'those skilled in this art thatvarious changes and modifications may be made therein withoutdeparting-tromthe spirit or scope of the invention.

We claim:

l. The process for making a cured elastomeric composition which.comprises reacting (1) the' elastomeric reaction product of (A),amaterial prepared from bitunctional ingredients including at' least onedibasic carboxylicacidand atleast one complementary bifunctionalreactant selected from the group consisting of glycols, amino alcohols,and diamines, the hydrogen-bearing amino groups being present in anamount not to exceed 30% of the total number of hydrogen-bearing aminogroups and hydroxyl groups present, said material having; ahydroxylnumber from-30 to 140' and an acid numberfrom 0 'to' 12, and (Bat least one diisocyanate selected from the group'consistin'g ofhexamethylene diisocyanate and'tetramethylenediisocyanate, thediisocyanate-being usedin' an amount ranging from 1.00 to 1.20 mols permol of said material, with (2) a sufiicient amount of atleast onepolyisocyanate'to bring the total of ---NC() equivalents" present insaid cured composition tofrom- 2.80 to 320 equivalents Of -NCO per molof said material.

21 The'pr'o'c'ess defined by'claim l in which (2) is a suflicient amountof at least one diisocyanateto bring the total amount ofdiisocyanatereacted with the material to from 1.4to 1=.6- mols per'molof said material.

3.-Theprocess defined byclaim l in which the material (-A)is-fapolyester prepared from bifunctional ingredients including. adipicacid,- ethylene glycol and propylene glycol.

4-. The process defined" by'claim 3-inwhich the material (A) is-a1polyester. prepared from approximately mol percent of: ethylene glycol,approximately 20 mol- References Cited in the file of this patent UNITEDSTATES. PATENTS Coffey et-a1. Aug. 5, 1952 Schmidt et a1. Dec. 9, 1952

1. THE PROCESS FOR MAKING A CURED ELASTOMERIC COMPOSITION WHICHCOMPRISES REACTING (1) THE ELASTOMERIC REACTION PRODUCT OF (A) AMATERIAL PREPARED FROM BIFUNCTIONAL INGREDIENTS INCLUDING AT LEAST ONEDIBASIC CARBOXYLIC ACID AND AT LEAST ONE COMPLEMENTARY BIFUNCTIONALREACTANT SELECTED FROM THE GROUP CONSISTING OF GLYCOLS, AMINO ALCOHOLS,AND DIAMINES, THE HYDROGEN-BEARING AMINO GROUPS BEING PRESENT IN ANAMOUNT NOT TO EXCEED 30% OF THE TOTAL NUMBER OF HYDROGEN-BEARING AMINOGROUPS AND HYDROXYL GROUPS PRESENT, SAID MATERIAL HAVING A HYDROXYLNUMBER FROM 30 TO 140 AND AN ACID NUMBER FROM 0 TO 12, AND (B) AT LEASTONE DIISOCYANATE SELECTED FROM THE GROUP CONSISTING OF HEXAMETHYLENEDIISOCYANATE AND TETRAMETHYLENE DIISOCYANATE, THE DIISOCYANATE BEINGUSED IN AN AMOUNT RANGING FROM 1.00 TO 1.20 MOLS PER MOL OF SAIDMATERIAL, WITH (2) A SUFFICIENT AMOUNT OF AT LEAST ONE POLYISOCYANATE TOBRING THE TOTAL OF -NCO EQUIVALENTS PRESENT IN SAID CURED COMPOSITION TOFROM 2.80 TO 3.20 EQUIVALENTS OF -NCO PER MOL OF SAID MATERIAL.